on stock motors your not going to notice any big differences. the idle may get smoother, you may pick up a slight bit of gas milage, and even a small amout of hp. all those gains will be so small that you probly wont notice. now if you run a higher compression motor, blower motor, or a nitrous motor, you will want some sort of strong ignition system.
The difference is this: An MSD Box is a capacitive discharge ignition module. What this means in simple terms is that it supplies multiple (4) sparks to your spark plugs each time they fire instead of the stock ignition single spark. This helps to better burn the fuel mix in the cylinder creating better cyl pressure and a more stable flame front.(more complete burn) The MSD boxes work really well They are worth the money on a souped up engine I would recommend it for a performance application or if you plan to upgrade in the future. Its better than a stock ignition but on a stock engine you wont reap the full benifits an MSD box can provide.
If your engine is more stock than a full race engine then a DuraSpark will be all you need. The MSD will work better if your compression ratio is in the 12 to 1 neighborhood.
The drawing posted by 'rthomas771' is dead on. Exactly how it needs to be connected. Want to illiminate everything external to the dist? Install a Pertronix III instead of the Pertronix I or II. It's a complete ignition system inside your dist. Has multistrike capability all the way to red line. Has a built in and settable rev limiter. Only slightly larger but still fits. And it's not much more than a Pertronix II. Still only 2 wires protruding form the dist. The MSD is a good system but this simpler and more compact. R
